Influence of weather and climatic conditions on the viticultural production in Croatia

Vinogradarstvo je poljoprivredna djelatnost pod izravnim utjecajem vremenskih i klimatskih prilika pa je vrlo osjetljiva na klimatske promjene. Glavni cilj bio je istražiti utjecaj vremenskih i klimatskih uvjeta na vinovu lozu i kemijski sastav grožđa te koji su parametri u vinogradarskoj proizvodnji već zahvaćeni klimatskim promjenama. Praćenjem četiri pokusna kultivara vinove loze: Graševina, Chardonnay, Plavac mali i Merlot analiziran je utjecaj vremenskih uvjeta na nastupe pojedinih fenofaza (pupanje, cvatnja, šara i berba) vinove loze i kakvoću grožđa. Odabrano je 57 pokusnih vinograda smještenih unutar granica 12 vinogradarskih podregija Hrvatske, a istraživanje je provedeno tijekom dvije uzastopne proizvodne vinske godine (2017. i 2018.). Na ukupno 208 uzoraka (104 uzorka u svakoj od analiziranih godina) analizirane su glavne uvometrijske karakteristike navedenih kultivara (dužina, širina i masa grozda te masa bobice). Na svježim uzorcima grožđa provedene su osnovne kemijske analize (sadržaj šećera, ukupne kiseline i pH vrijednost), a na uzorku bobica podjednakog sadržaja i zrelosti provedena je analiza aromatskog (bijeli kultivari) i polifenolnog (crni kultivari) sastava grožđa. Za sve izmjerene i utvrđene vrijednosti provedena je statistička analiza. Sa 79 meteoroloških postaja DHMZ-a korišteni su i obrađeni podaci minimalne, maksimalne i srednje dnevne temperature zraka za izračune srednje temperature zraka u vegetacijskom razdoblju (engl. Average growing season temperature ; GST, °C), Winklerovog indeksa (engl. Growing degree-days; GDD, °C), Huglinovog indeksa (HI, °C) i indeksa hladnih noći (CI, °C). Određeni su trendovi agroklimatskih indeksa za razdoblje 1961.–2018. Prostorne raspodjele agroklimatskih indeksa prikazane su s finom horizontalnom razlučivosti od 1 km. Nedostajući dnevni meteorološki podaci na nekoj postaji interpolirani su pomoću dnevnih podataka susjednih postaja. Karte četiriju agroklimatskih indeksa u razdoblju 1989.–2018. i usporedba s referentnim klimatskim razdobljem 1961.–1990. pokazale su povećanje promatranih indeksa u posljednjih 30 godina. To potvrđuje činjenicu da su područja uzgoja vinove loze u Hrvatskoj raspoređena unutar četiri vinogradarske zone (B, C I, C II i C III). Linearni trendovi promatranih fenofaza vinove loze ukazuju na njihov sve raniji početak, osim fenofaze šare te su oni izraženiji u kontinentalnom dijelu Hrvatske. Opaženi porast temperature zraka u Hrvatskoj posljednjih 30 godina utječe na skraćivanje razdoblja dozrijevanja grožđa od šare do berbe promatranih kultivara vinove loze, povećanje sadržaja šećera i smanjenje ukupne kiseline u moštu kultivara Graševine i Chardonnaya. Prikazani rezultati povećanja agroklimatskih indeksa pokazali su nužnost revidiranja svih vinogradarskih zona u Hrvatskoj što je već potaknulo daljnja istraživanja za izradu nove regionalizacije vinogradarskih područja Hrvatske.Viticulture is an agricultural activity directly influenced by weather and climate conditions, and is therefore very sensitive to climate change. The objective of the research was to investigate the impact of weather and climatic conditions on the vine and the chemical composition of the grapes, and to determine which parameters in viticulture production are already affected by climate change. The influence of weather conditions on the occurrence of individual phenophases (budding, flowering, pattern and harvest) of grapevine and grape quality was analysed by monitoring four experimental grape cultivars: Graševina, Chardonnay, Plavac mali and Merlot. Graševina, as the most represented vine cultivar in Croatia, covers 25 % of total vineyards, while Plavac mali, as the third cultivar in terms of total representation, i.e., as the most represented red cultivar, covers 8 % of the total vineyards in Croatia. Cultivars Chardonnay and Merlot are taken as examples of international varieties that are represented in all wine-growing regions of Croatia due to their pronounced ecological adaptability. In addition, Merlot in fourth place with 5 % and Chardonnay in sixth place with 4 % of the total area planted, are among the 20 leading grape varieties by planted area. 57 experimental vineyards located within the borders of 12 wine-growing sub-regions of Croatia were selected, and the research was conducted during two consecutive wine production years (2017 and 2018). The main criterion for selecting the location of the research, apart from the assortment in the vineyard, was that the locations are situated as close as possible to the meteorological station from which the data for determining agroclimatic indices were processed.The main uvometric characteristics of these cultivars (length, width and weight of grapes and weight of berries) were analysed on a total of 208 samples (104 samples in each of the analysed years). Basic chemical analyses were performed on fresh grape samples (sugar content, total acids and pH value), and on the sample of berries of equal content and maturity, the analysis of aromatic (white varieties) and polyphenolic (red varieties) composition of grapes were performed. Statistical analysis was performed for all measured and determined values. For four experimental cultivars, for the period 2001-2018, i.e. 2007-2018, an earlier start of the harvest and a higher sugar content are shown, except for the Merlot cultivar at the Blato location, where the harvest is later and the sugar content is lower. On the long-term series of phenological data of the DHMZ in the period 1961-2018 on the cultivars Graševina and Plavac mali at the locations Daruvar and Križevci, i.e. Hvar and Orebić, the earlier beginning of budding, flowering and harvesting is noticed, and the beginning of ripening (pattern) is late. Considering that the phenophase of the pattern begins mainly in August, when the air temperature values are extremely high and there is a lack of precipitation, it can be concluded that this is the reason for the delay of this phenophase. Nevertheless, the harvest is earlier for both cultivars, which is more visible on the continent. Minimum, maximum and mean daily air temperature data were used and processed from 79 DHMZ meteorological stations for calculations of average growing season temperature (GST, °C), Winkler index (Growing degree-days; GDD, °C units), Huglin heliothermal index (HI, °C units) and the cool night index (CI, °C). Trends in agroclimatic indices for the period 1961–2018 have been determined. Spatial distributions of agroclimatic indices are presented with a fine horizontal resolution of 1 km. Missing daily meteorological data at a station are interpolated using the daily data of neighbouring stations. Maps of four agroclimatic indices in the period 1989-2018 and comparison with the reference climate period 1961–1990 showed an increase in the observed indices in the last 30 years. This confirms the fact that the areas of vine cultivation in Croatia are distributed within four wine-growing zones (B, C I, C II and C III) according to Winkler index. The linear trends of the observed phenophases of the vine give an earlier and earlier beginning, except for the phenophase of the pattern, and they are more pronounced in the continental part of Croatia. The observed increase in air temperature in Croatia over the last 30 years has shortened the period of grape ripening from pattern to harvest of observed grape cultivars, increased sugar content and reduced total acidity in the must of Graševina and Chardonnay cultivars. According to the division of the Huglin index (HI) in the vegetation period from the beginning of April to the end of September in the wine-growing zones of Croatia in the periods 1961–1990 and 1989–2018, results indicate that northern and central geographical regions belong to the predominantly temperate, while other wine-growing areas belong to the moderately warm area for grapevine cultivation. In addition, comparing the obtained mean HI values between the two mentioned periods, they show its increase from approximately 200 to 300 °C in the recent period. A comparison of the uvometric data of these two harvests showed that the average values of mass, width and length of the cluster, the mean mass of one berry and the number of berries per bunch in 2018 are significantly greater than in 2017. In the 2018 harvest, the mean values of mass, length and width of the cluster, the mass of one berry and the number of berries per cluster were greater than the values of the variables in the 2017 harvest. The reason for this can be related to the extremely hot and very dry summer of 2017 (in most of the mid-Adriatic even extremely dry) and the cold and rainy (in the mid-Adriatic even extremely rainy) September. The presented results of the increase in agroclimatic indices have shown the need to revise all wine-growing zones in Croatia, which has already prompted further research to develop a new regionalization of Croatian wine-growing areas. Due to the increase in air temperature, continental Croatia has become suitable for planting wine cultivars that need more heat, and in the future there will be the possibility of raising vineyards of early grape cultivars in mountainous Croatia. However, if such a positive trend in air temperature continues, the cultivation of our most widespread cultivar Graševina and its quality wine production will become questionable in the future